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Geant4 Hadronic Physics Working Group Meeting
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Description
Monthly Geant4 Hadronic Physics Working Group meeting
Geant4 Hadronic Physics Working Group Meeting
Discussion meeting
Introduction of the discussion meetings (Pico)
Pico introduced a Discussion Block to make a quick round table pass on activity (or not) on the various long term items and long standing issues in Hadronic Physics in Geant4.
Pico's idea is to cancel the least amount of monthly meetings because we do not have what he calls "formal contributions". He was happy with the length of the meeting today (circa 30 minutes). He also says that he understands that most members are in the northern hemisphere and the meetings on July and August are OK to be cancelled given the potential low activity and likely low attendance. The minutes like this one are not a full replacement of the actual conversation.
Alvaro shared a list with Pico (not disclosed in the meeting. Only mentioned in passing) of "long term items" that he would like us (as hadronics) to keep an eye on. It is Pico's understanding that he himself can act on a number of them.
Pico proposed to add minutes ( like this one ;-) ). At the end of the meeting, Krzysztof made a point about wanting the minutes also.
Proposed GitHub Pull Request for Bertini (Alberto and Julia)
These are the two GitHub pull request by Tamas Vami from the LDMX collaboration. Although independent code inspection by Julia and Alberto suggests that they "look correct" and they "should only affect the parts they claim they affect" it has been deemed too risky to include them so close to the release of 11.5. Both PR will be integrated soon after the release with the idea to be shipped with the 11.5.patch01 once their performance have been validated and no noticeable unexpected side effect occur.
Bertini: meson first in gamma n two-body states
[From the PR messsage]:
G4CascadeFinalStateAlgorithm::GenerateTwoBody gives the CM angle sampled from the two-body angular distribution to the first particle of the final state. Since 10.5 the gamma p two-body states list the meson first ({pi0,pro}, {pip,neu}, {kpl,lam}, ...), so the forward-peaked gamma N -> N pi distribution goes to the pion. The gamma n states were not changed and still list the nucleon first ({neu,pi0}, {pro,pim}, {lam,k0}, ...), so in gamma n -> N pi the nucleon gets the forward-peaked pion distribution.
This PR lists the meson first for gamma n too, for both N pi and K Lambda/Sigma. Cross sections are unchanged (gamma n shares the gamma p table).
Test: free gamma N collisions with G4ElementaryParticleCollider at 5.6 GeV, 200k each. Fraction of N pi final states with the nucleon forward in the CM:
before with this PR
gamma p 0% 0%
gamma n 100% 0%
Bugzilla: https://bugzilla-geant4.kek.jp/show_bug.cgi?id=2783
Bertini: forced particles choose the target by inverse mean free path
[From the PR]:
For forced particles (incident photons and muons, G4NucleiModel::forceFirst), generateInteractionLength always returns a path inside the zone. In generateInteractionPartners every candidate target (p, n, and the pp, pn, nn dinucleons) gets its own forced path and the shortest one wins. With forced paths the winner no longer reflects the relative cross sections: targets with small inverse mean free paths are strongly over-selected. For incident photons this over-produced photo-absorption on quasi-deuterons by one to two orders of magnitude.
With this PR, forced particles get one interaction point from the total inverse mean free path, and the target is picked in proportion to its inverse mean free path. All other particles keep the current path-based selection, so hadron-nucleus results are unchanged.
The algorithm is by Natalia Toro (SLAC). The LDMX experiment has used it since 2018 for photonuclear simulation of GeV photons on tungsten, which drives its dominant background
Bugzilla report: https://bugzilla-geant4.kek.jp/show_bug.cgi?id=2784
Changed default FermiBreakUp model (Alberto)
[Copied from the MR text, See the Merge Request for more details.]:
In the file G4DeexPrecoParameters.cc, changed the default FermiBreakUp model, from G4FermiBreakUpVI to G4FermiBreakUpAN. This allows to test the new FermiBreakUp model. Based on the results of the next monthly reference tag, 11.4.ref10,a decision will be made on the default FermiBreakUp model for the release 11.5.
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